JOHN DUNCAN. (2019). ASTRONOMY (2016 Ed.). PARRAGON BOOK PUBLISHERS.
Lua i Stíl Chicago (17ú heag.)JOHN DUNCAN. ASTRONOMY. 2016 Ed. LONDON: PARRAGON BOOK PUBLISHERS, 2019.
Lua MLA (9ú heag.)JOHN DUNCAN. ASTRONOMY. 2016 Ed. PARRAGON BOOK PUBLISHERS, 2019.
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